Blender export support for 3MF (or AMF) file format?
This is a tough one. My concern about most of the answers that I see on the Blender forums is that people don't get that 3MF is NOT like STL, it allows for actual bitmaps for textures, not just one flat color.
So, I do have a workflow for you, that will at least get your model out, if you are running Windows 10.
Setup Blender to export to GLTF. Export a binary GLTF (GLB).
Open the Windows 3D builder app. It's free.
Open the GLTF with 3D Builder.
Then export a 3MF.
I tested it with Simplify3D and it seemed to work fine. The model sliced fairly easily.
    == John ==